First, I must commend you on putting in such a large amount of polish. I can tell despite the simplicity of the game a lot of work has been done to make it feel fantastic. The graphics look great, the sound effects and feedback are incredible.
Best of all, is the insanely addictive gameplay loop. It gives me the same feeling as something like peggle or breakout. After a little bit it did start to feel pretty repetitive though. I think with just a couple things though you could have had me playing for hours!
1st, I think you need to work on adding some new powerups and unique mechanics. You could explore things like breaking up the players circle into multiple smaller ones, adding a bounce, changing movement speed, jump height, gravity, etc.
And I also think you should add some kind of progression or goal. Right now it feels like I have no reason to keep playing past the simple gameplay loop. As good as it is, it wont keep players around for long enough. I would look at how games like Peggle solve this, and try adding some things like increasing difficulty / complexity as you level up. You could also try adding some kind of score system, but I think the problem now is there is no way to "lose" which trivializes the score in a way.